The present invention relates to pectin and a method for its production, as well as to acidic foods incorporating it and to a method for their production. More specifically, the present invention relates to pectin obtained from root vegetables and especially potatoes, to a method for its production, to acidic foods such as acidic protein drinks, acidic dairy beverages, acidic frozen desserts and acidic desserts obtained by adding citrus juices or other fruit juices, organic acids or inorganic acids to protein drinks such as milk and soy milk, as well as coffee beverages, lactic acid bacteria beverages, liquid yogurt and the like, and to a method for their production.
Root vegetables, and potatoes in particular, have long been known to contain pectin substances in combination with starch (Ullmanns Enzyklopaedie der techn. Chemie, Bd. 13, 171, Urban and Schwarzenberg, Muenchen-Berlin (1962)), and many studies have been carried out on their use as raw materials for production of pectin (Die Staerke 26 (1974) 12, 417-421, CCB 3, 1(1978) 48-50; Getreide Mehl und Brot. 37, 5(1983) 131-137; Japanese Unexamined Patent Publication SHO No. 60-161401; Chem. Eng. Technol. 17(1994) 291-300; WO 97/49298). Research has also been carried out for years on its uses, with most studies focusing on its use as a gelling agent (ZSW Bd. 31(1978) H.9 348-351, Getreide Mehl und Brot 37, 5(1983) 131-137, WO 97/49298).
As mentioned above, production of pectin from potatoes has long been studied as a research topic. However, in terms of its function as a gelling agent for jams and the like that has been examined as a major use, it has not excelled over pectin derived from fruits such as apples and citrus fruits, and its use has therefore not been practical to date. The uses and production methods for fruit-derived pectin have therefore been studied, but there has been virtually no research to date on the unique functions or detailed production conditions for pectin derived from root vegetables, and potatoes in particular.
Production of acidic protein foods has traditionally employed apple- and citrus fruit-derived pectin, water-soluble soybean polysaccharides, carboxymethylcellulose sodium, propyleneglycol alginate and the like for the purpose of preventing aggregation and precipitation of protein particles. However, when using any of these stabilizers, dispersion of the protein can only be satisfactorily stabilized in a pH range below the isoelectric point of the protein, and a problem has existed in that there are no stabilizers that can stabilize acidic protein foods in the acidic pH range exceeding the isoelectric point.
On the other hand, it has been reported that in the weakly acidic pH range of from neutral to pH 5.2, addition of an organic acid salt can stabilize the protein components (Japanese Examined Patent Publication HEI No. 5-52170), but even with this proposal the emulsifying property of the stabilized protein solution is lost, and the effect of the added organic acid salt makes it impossible to achieve satisfactory acidity.
In addition, lactoproteins in acidic dairy beverages such as xe2x80x9cyogurt drinksxe2x80x9d, lactic acid bacteria beverages and fruit-added milk are extremely unstable, such that the lactoproteins aggregate and with passing time produce lactoprotein precipitates, resulting in separation of the whey. Upon heat sterilization, the aggregates become notable resulting in total loss of the product value.
Also, dairy component-added coffee, for example, that is transportable at ordinary temperature, has traditionally been produced through a procedure whereby the raw materials such as coffee extract, dairy components, sugars, emulsifiers, etc. are mixed and dissolved to make a coffee preparation, and then passed through a homogenizer and heated to 110-135xc2x0 C. for sterilization, either before or after packing into a storage container; however, the high temperature of the heating step causes a decomposition reaction of the coffee components, and lowers the pH of the coffee solution. Thus, when the pH of the solution is lowered, giving it an acidity of pH 6.0 or below, the lactoproteins in the dairy components contained in the coffee solution are denatured resulting in separation and aggregation, so that the product value is lost. In order to prevent denaturation of the lactoproteins, an alkali substance such as sodium bicarbonate is often added beforehand to the coffee solution to adjust the pH of the coffee solution to greater than pH 6.5 prior to the heating step, but since dairy component-added coffee prepared by such a method is heat sterilized with the pH at greater than 6.5, the aroma of the coffee is altered, resulting in the characteristic aroma and flavor of retorted can coffee which is different from the original regular coffee.
On the other hand, there is a strong demand for development of heat-sterilized dairy component-added coffee beverages that can be stored at ordinary temperature and still have excellent taste with acidity, and methods for production of dairy component-added coffee beverages with acidity have been proposed such as a method of using fresh cream, butter or the like as dairy components and adding emulsifiers such as sucrose fatty acid esters and crystalline cellulose (Japanese Unexamined Patent Publication HEI No. 6-245703) and a method of using acidic polysaccharides to stabilize the lactoproteins (Japanese Unexamined Patent Publication SHO, No. 62-74241); however, none of these methods have been successful at stabilizing dairy components without losing the unique coffee taste and properties.
Thus, because coffee exhibits the characteristic aroma and acidity of regular coffee in a weak acidic pH range of pH 6.5 and below, a problem occurs when the pH of a coffee solution is modified during preparation and is kept at above pH 6.5 as it loses the characteristic aroma and acidity of regular coffee, while the coffee obtained upon heat sterilization undergoes a drastic deterioration in taste as compared to the original regular coffee. In other words, no technique has existed in the prior art that can stabilize dairy components over long periods in order to avoid losing the characteristic taste and properties of regular coffee.
As mentioned above, there exist techniques for achieving stabilization of protein dispersion in the pH range below their isoelectric point and in the pH range of from pH 5.2 to neutral, but at the current time there is no technique available that can satisfactorily stabilize acidic protein foods in a general pH range of higher acidity than the protein isoelectric point.
It is an object of the present invention to provide a unique pectin obtained from root vegetables, and potatoes in particular, and to a method for its production, as well as acidic protein foods that are stable in an acidic pH range above the isoelectric point of the protein and a method for their production, in order to thereby provide heat sterilized dairy component-added beverages that have stable dairy components over long periods and that can be transported at ordinary temperature. Here, xe2x80x9cacidityxe2x80x9d will refer to the pH range of 6.5 and lower.
As a result of diligent research aimed at overcoming the problems mentioned above, the present inventors have found that a unique function is expressed by pectin obtained by hot water extraction under weak acidic conditions from starch pulp as a processing by-product of potatoes. In particular, it was discovered that using white potato-derived pectin allows acidic protein foods to be satisfactorily stabilized in a pH range above the isoelectric point of the protein, at a lower viscosity than with fruit-derived pectin. The present invention has been completed on the basis of this discovery.
The present invention therefore provides a method for production of pectin that comprises hot water extraction from root vegetables under weak acidic conditions of pH 3.8-5.3 and pectin produced by the method, as well as a method for production of acidic protein foods comprising addition of this pectin to acidic protein foods, and acidic protein foods produced by the method.
According to the invention, the root vegetables as raw materials for extraction of pectin may be, for example, potatoes such as white potatoes, sweet potatoes, taros, yams, konjak, etc. or burdocks, carrots, Japanese radishes, lotuses, beets and the like, but potatoes are particularly preferred. These potatoes may be used directly either in raw or dried form, but it is preferred to use the raw or dried starch pulp produced as a processing by-product from starch production.
The extraction of pectin from the raw material must be carried out under weak acidity of from pH 3.8 to pH 5.3. Pectin extracted outside of this pH range does not exhibit the protein dispersion-stabilizing function exhibited in a pH range above the isoelectric point.
Incidentally, while the reason for this exhibited function of pectin extracted in the aforementioned pH range cannot be explained in full detail, it is surmised that it probably has to do with the degree of esterification of the polygalacturone chains and the three-dimensional structure of the neutral sugar chains in the extracted pectin.
The extraction of pectin in this pH range is preferably carried out at a temperature of 100xc2x0C. or higher. When the extraction is carried out at a temperature of below 100xc2x0 C., more time is required for elution of the pectin and an economical disadvantage is therefore presented. On the other hand, extraction at higher temperature can be completed in a shorter period, but if the temperature is too high an adverse effect may be produced on the flavor and color tone while the pectin will be converted to a lower molecular weight thus reducing the effect exhibited by its function, and therefore the temperature is preferably no higher than 130xc2x0 C.
The purity of the pectin of the invention may be increased by removing the contaminating starch substances, to allow stronger expression of the function. The contaminating starch substances are preferably present at no greater than 60%, and more preferably no greater than 50%, based on the measured content by quantitation using enzymes. The starch substances may be removed by a publicly known method, and as an example there may be mentioned decomposition by enzymes, washing removal from the raw material using water at 100xc2x0 C. or below, and separation of the insoluble portion in the extract. Pectin with any molecular weight value may be used, but it preferably has an average molecular weight of from a few tens of thousands to a few million, and more specifically from 50,000 to 300,000. The average molecular weight of the pectin is the value determined by the limiting viscosity method which measures the viscosity of a 0.1 molar NaNO3 solution using standard pullulan (Showa Denko, KK.) as the standard substance.
The pectin derived from root vegetables, and particularly potatoes, obtained according to the invention has a unique function differing from conventional pectin derived from fruits such as apples or citrus fruits. Specifically, while the function of fruit-derived pectin that can stabilize protein dispersion in a pH range below the isoelectric point is utilized to provide a stabilizer for acidic dairy beverages, the pectin of the invention has a function that can stabilize protein dispersion in a pH range above the isoelectric point, and this function therefore allows production of acidic protein foods that are stable in a pH range above the isoelectric point, which have not been obtainable according to the prior art.
The acidic protein foods of the present invention are acidic foods containing animal and vegetable proteins, and they include protein products with acidity, for example, acidic protein beverages obtained by adding citrus juices or other fruit juices, organic acids such as citric acid or lactic acid, or inorganic acids such as phosphoric acid, to beverages using animal and vegetable proteins, such as milk and soy milk; acidic dairy beverages obtained by rendering dairy products acidic; acidic frozen desserts such as acidic ice cream or frozen yogurt obtained by adding fruit juices or the like to frozen desserts containing dairy components; acidic desserts obtained by adding fruit juices or the like to gelled foods such as pudding and Bavarian cream, as well as coffee beverages, lactic acid bacteria beverages (including live bacteria and pasteurized types), fermented milk (in solid or liquid form), and the like. xe2x80x9cAnimal and vegetable proteinsxe2x80x9d refers to cow milk, goat milk, skim milk, soy milk and their powdered forms of whole powdered milk, skim powdered milk and powdered soy milk, as well as sweetened milk to which sugar has been added, concentrated condensed milk, processed milk fortified with minerals such as calcium or vitamins, and fermented milk and to proteins derived therefrom. xe2x80x9cFermented milkxe2x80x9d refers to fermented milk obtained by sterilizing the aforementioned animal or vegetable protein and then adding a lactic acid bacteria starter for fermentation, but if desired this may be powdered, or sugar may be added thereto.
The amount of the pectin of the invention used may be, as a standard, about 0.05-10 wt % and preferably 0.2.-2 wt % with respect to the final product, but this may be varied depending on differences in the protein concentration, and therefore the amount thereof used is not restricted for the invention.
For the production of acidic protein foods according to the invention, stabilizers common to the prior art may also be used, for example, pectin derived from apples or citrus fruits, water-soluble soybean polysaccharides, carboxymethylcellulose sodium, propyleneglycol alginate, carrageenan, microcrystalline cellulose, chitosan, organic acid salts, polyphosphate salts, emulsifiers, heat denatured proteins and the like, which can further widen the stable pH range.
The present invention will now be explained in greater detail by way of examples, which are only illustrative and are not intended to limit the scope of the invention in any way. Throughout the examples, the parts and percentages are based on weight.